Sharp Pelvic Dissection for Abdominoperineal Resection for Distal Rectal Cancer Based on Anatomical and MRI Knowledge

Kim, Nam Kyu

Abstract

Even though sphincter saving surgery such as coloanal anastomosis or intersphincteric resection have been popular in era of Total Mesorectal Excision (TME) in distal rectal cancer, unreasonable sphincter saving surgery might cause a couple of troublesome complications in terms of oncologic or functional outcomes. Since preoperative staging work up recently have been developed with MRI or MDCT, it is important to assess whether rectal cancer invaded into surrounding sphincter or levator ani muscle based on MRI or MDCT coronal image study. If tumor is located at a very close distance or has invaded the adjacent sphincter muscle, the need of abdominoperineal resection is definite without any hesitation for curative resection. But, the actual number of cases of APR have been decreased in favor of sphincter preserving surgery even APR remains an important therapeutic option in the surgical treatment of low rectal cancer. Indication case for APR have become a intersphincteric resection or ultralow anterior resection and coloanal anastomosis Even patients who showed invasion of sphincter underwent sphincter saving surgery, lately proven safe in terms of recurrence and defecation functions. On practical view points on operative techniques, abdominal phase are same as TME techniques. Sharp pelvic dissection must be carried out along the visceral fascia enveloping the mesorectum to the levator ani muscle with preservation of pelvic autonomic nerve. Perineal phase dissection is a key process in APR. During perineal dissection, inadequate resection margin and blunt tissue dissection along the nonanatomical plane encourage implantation of a malignant cell and local recurrence. Moreever, it could lead to serious complications such as prostatic urethral injury, vaginal wall perforation, perineal sinus and fistula. Massive bleeding from pelvic side wall major vessels injury. Especially in males with very narrow pelvis, pelvic dissection is very difficult due to deep narrow and blunt sacral curvature of the pelvis. It is nearly impossible to reach the levator ani muscle and result in perineal dissections performed on excessively high levels. For colorectal surgeons with insufficient experience, it is difficult to dissect the rectum from the perineum upto the seminal vesicle level. In the classic pattern, anterior and lateral dissection from the prostate or vagina after the completion of posterior dissection. The dissected proximal colon was delivered outward through the perineal wound and with traction of the delivered portion of the colon, anterior dissection was performed. However, in patients with narrow pelvis, such delivery of the proximal colon through perineal wound can result in fractured tumor and local recurrence due to limited operation field. Therefore, it is mandatory that specimen must be delivered in situ after posterior, anterior and lateral dissection. During posterior dissection, gluteus muscle must be observed and removal of the ischiorectal fat tissue should be accomplished. In lateral dissection, levator ani muscle must be divided near the bony insertion. Finally, during anterior dissection, seminal vesicle and prostate gland must be exposed and neurovascular bundle observed at the 10 and 2 o'clock direction. In addition to TME on abdominal phase, Sharp Anatomical Perineal Dissection (SAPD) empowered by 3D concept based on MRI is a key process for prevention of local recurrence in APR.